The invention relates to a projection system with a light tunnel that can uniformize brightness distribution of a light from a light source of the projection system, and in particular, to a light tunnel that can be easily held and applied to various projection systems with various light sources and image generation devices.
The conventional optical projection system is widely applied to presentation and entertainment. During operation, a light source thereof generates a light passing through an image generation device that changes the light to different hues and brightness. The light passing through the image generation device is projected to a screen so that audiences can see projected images.
Referring to FIG. 1, a conventional optical projection system 1 comprises a light source 10, a color wheel 11, a light tunnel 12, a transmission lens 14, an image generation device 16, and a projection lens 18. The light source 10 generates a light through the color wheel 11, the light tunnel 12, and the transmission lens 14 consecutively. Then, the light is projected to the image generation device 16, such as a digital micromirror device (DMD) with a plurality of pixel mirrors (not shown) that can be activated and deactivated. Specifically, according to digital signals for the required images, the pixel mirrors can be rotated respectively to generate required pixel brightness. After the color wheel 11 provides the required pixel brightness, the images based on the digital signals are obtained. Then, the light is projected to a screen 20 via the projection lens 18 so that audiences can see projected images. Additionally, rather than the digital micromirror device, the image generation device may be a liquid crystal display (LCD). Since the liquid crystal display can inherently adjust the hue and brightness of the light, the color wheel can be omitted. Generally speaking, brightness distribution of the light from the light source 10 is not uniform, such that brightness at the center of the display exceeds that at the edges. The light tunnel 12 is provided to overcome the above problem.
The conventional light tunnel 12 comprises four reflectors as shown in FIG. 2. To assemble the light tunnel 12, each reflector contacts each other at each edge, and adhesive 13 is coated at space between each edge. FIG. 6A is a cross section of the light tunnel 12. Two sets of reflectors 120, 120′ are combined to a rectangle to form a light entrance 122 and a light exit 124. The adhesive 13 may be epoxy, silicon rubber, or ultra-violet (UV)-curved adhesive. Inner surfaces of both reflectors 120, 120′ reflect the light. Both reflectors 120 have same area. Both reflectors 120′ have same area. Based on the application, the area of the reflector 120 may be the same as or different from that of the reflector 120′. Thus, after the light enters the light tunnel 12 from the light entrance 122, it is reflected by the inner surfaces of the reflectors 120, 120′ repeatedly. Then, the light emitted from the light exit 124 is thus more uniform in brightness distribution. FIG. 4A is a schematic view of brightness distribution of the light before/after passing the light tunnel 12, wherein arrow X represents position, and arrow Y represents brightness of the light. The brightness distribution of the light before entering the light entrance 122 is shown on the left of the light tunnel 12, wherein the brightness at the center clearly exceeds that at the edge. The brightness distribution of the light emitted from the light exit 124 is shown on the right of the light tunnel 12, the brightness at the center being substantially equal to that at the edge, providing uniform in brightness distribution accordingly.
Since the cross section of the light entrance 122 is the same as that of the light exit 124, attachment of the light tunnel 12 to various light sources or other devices can be difficult. Thus, another conventional light tunnel 32 is provided, as shown in FIG. 3A, comprising four reflectors, two of which are labeled as 320, and the other two as 320′. The reflectors 320 are trapezoid and opposite to each other. The reflectors 320′ are rectangular and opposite to each other. Thus, the light tunnel 32 is trapezoidal with a light entrance 322 and a light exit 324. FIG. 3B shows top and side views of the light tunnel 32. As a result, the light tunnel 32 can be combined with various light sources, image generation devices, and other devices. FIG. 4B is a schematic view of brightness distribution of the light of the light tunnel 32. Since the conventional light tunnel is disclosed in U.S. Pat. Nos. 5,625,738 and 6,332,688, its detailed description is omitted.
Generally speaking, the light tunnel must be precisely positioned in the optical projection system so that the light processed thereby can be projected to a predetermined position. If the light tunnel is not properly positioned, the accuracy of the projected image is affected. Since the light tunnel 32 comprises non-parallel edges at its sides, it is difficult to precisely align during manufacture. Even if the light tunnel is precisely aligned, it can further be dislocated by vibration or other factors, also resulting in imprecise projection. Moreover, as shown in FIG. 6A, the adhesive 13 at the edges of the light tunnel often protrudes from the outer surfaces of the reflectors 120, 120′. Thus, it is difficult to hole the light tunnel due to the protruding adhesive. As a result, it is desirable for a light tunnel that can be easily held and applied to various projection systems with various light sources and image generation devices.